1. Technical Field
This invention generally relates to an ink supply system and method of supplying ink, and more specifically relates to a method and system for supplying ink to a print head at substantially constant static pressure.
2. Background Art
The present invention is particularly well suited for use with sophisticated ink jet printers, although it is not limited to use with such printers. With these sophisticated ink jet printers, it is desirable to produce extremely high quality images on wide webs of paper or other printable surfaces as the surfaces move at very fast printing rates relative to printing heads. The requirements of these sophisticated ink jet printers in terms of accuracy of paper feed, methods of paper feed, and print head to paper distance are much higher than in conventional ink jet printers and pose problems not encountered in conventional printers.
There are conventional ink supply systems for sophisticated ink jet printers. However, several problems arise from use of these conventional ink supply systems. For example, in some systems a single supply must be used for all sub-reservoirs. In other systems, air is introduced into the ink within the sub-reservoirs, especially during priming of the system. In still other systems, the supply system includes one print head for each sub-reservoir, which increases the complexity and cost of the system. In yet other systems, the supply system is prone to surges of ink within the system.
In commercial ink jet printing applications, sophisticated ink jet printers are typically needed having a large printing area to permit printing of a large image on a target surface without multiple passes of the surface past the printing head. Furthermore, printing often must be done on a surface that is in some orientation other than horizontal. This requires a single print head using staggered ink inlet heights or multiple, smaller print heads with each head at staggered heights. However, for such non-horizontal print head arrangements, problems exist associated with the control of static pressure, and their commercial advantages have heretofore been limited by increasing costs or complexity relating to ink storage and delivery.
It is not feasible to supply a single print head using staggered ink inlet heights or multiple, smaller print heads with each head at staggered heights from a common reservoir because substantially uniform static pressure cannot be achieved (i.e. ink inlets or print heads disposed above the common reservoir fluid level experience negative static pressure, while those disposed below the reservoir experience positive static pressure). While it is feasible to provide each ink inlet or print head with a separate, level-controlled reservoir, the cost of such an arrangement is prohibitive. Additionally, the space limitations and tight spacing between print heads make it physically impractical to install reservoirs and level-control devices in this configuration.
Accordingly, what is needed is an ink supply system which may be easily and inexpensively constructed and a method of supplying ink which provides substantially constant and dependable control of the static pressure of ink delivered to a single print head using staggered ink inlet heights or to multiple, smaller print heads with each head at staggered heights.